Optical display system for augmented reality and virtual reality

ABSTRACT

Optical display systems and methods for providing three-dimensional and two-dimensional convergence corrected images to a user are described. The optical display systems may include at least two image generators producing a plurality of rays forming a plurality of images. A diffraction enhanced imaging system may be configured to collect the rays produced and control convergence angle of each ray at specific wavelengths into an optical waveguide. An in-coupling diffraction system may couple the rays into the optical waveguide. A wavelength compensated beam expander may expand horizontal extension of the images and an output coupling and vertical expansion system may magnify the images in a vertical direction and direct light towards a user at specific angles creating a wide field of view.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of U.S. Ser. No. 62/458,808,filed Feb. 14, 2017, and U.S. Ser. No. 62/547,352, filed Aug. 25, 2017,which are hereby incorporated by reference in their entirety.

BACKGROUND

Augmented reality (AR) and virtual reality (VR) systems promise torevolutionize the way humans interact with each other and the worldaround them. These technologies provide human eyes additionalinformation that either augments or supplant visual information receivedfrom the outside world to entertain, inform and/or educate a user.Generally, VR systems immerse a user in a virtual world, limiting inputfrom the outside world, and AR systems superimpose information and/orvirtual images onto a scene observed by a user. The user may be allowedto engage in interactive games, view information (e.g., instructionmanuals, handbooks) while performing a task or exploring, conductvirtual training, and/or visualize digital information. For example, ARsystems may use a head's up display (HUD), overlaying the outside worldwith images and/or data screens containing information adding to auser's experience.

In general, AR displays consist of four common main subsystems, each ofwhich may impact the display performance. First, the optical systemgenerates, manipulates and presents images to the viewer in a mannerthat causes a user to perceive existence of virtual objects within anoutside visual world. Second, environmental mapping may use cameras andsensors to obtain knowledge of the surrounding environment, such aswalls, desks and other surfaces that could support images and detect auser's movement within the environment. Third, head and eye trackingsystems may provide feedback on where a user wishes to look and theexistence of any alignment issues for which the system must accommodate.Finally, extensive software and hardware processing systems may containthe computing power that controls, coordinates, and drives the actionsof the other three subsystems.

Design and implementation of the optical system generally use eitherbulk optics systems or waveguide systems. Bulk optical systems use acombination of lenses and custom designed prisms to magnify anddistribute the image to a user's eye. The image generator projects lightinto a free-form prism—the shape of the prism deviates from regulargeometric figures—and total internal reflection (TIR) at the surfacecombined with the shape provides the means to magnify the image anddirect the magnified image toward a user's eye. A second prism placednearly in contact with the first prism corrects distortions caused bythe first prism and may allow light from the external world to passthrough to a user's eye. This solution possesses several drawbacks thatmay limit use for practical applications, including the large size andweight of the prisms, incomplete correction of image distortions, smallfield of view (FOV), and no practical path to implementing methods toresolve vergence-accommodation conflict. Examples of this type of systeminclude multi-focal plane displays and Google Glass, manufactured byGoogle having a principle place of business in Mountain View, Calif.

The more current offering of AR head-mounted displays use an opticalwaveguide system to connect the output of the image generator to auser's eye. The waveguide generally may consist of a piece of glass cutthin in one dimension, typically in width. Light rays propagate throughthe waveguide by TIR, and optical elements placed within the waveguideor along the walls of the waveguide provide means to couple light intothe waveguide from the image generator, modify the magnification anddivergence of the image, and couple the light out of the waveguidetowards the user's eye.

Present waveguide systems use either diffractive or reflective opticalelements in conjunction with the waveguides. Reflective elements possessan advantage of operating at all RGB wavelengths, greatly reducing thenumber of waveguides needed. Current implementations of such systems,however, suffer from bulkiness and scattering that may deteriorate imagequality. Most systems may utilize diffractive optical elements toovercome the size and scattering constraints of the reflective elements.Diffractive elements consist of periodic variations in the waveguide'srefractive index (holographic optical elements or HOEs), periodicvariations in the surface structure, created by patterning or cutting ofmaterial on the waveguide surface, computer-generated holograms (CCH),sub-wavelength digital elements (SWE) or dynamic diffractive optics.

Diffractive elements may present many advantages, including small sizeand weight, the ability to create them directly on or within thewaveguide, the ability to tune the element to pass light from theexternal scene with minimal distortion or dimming, and ease of design.Diffractive elements also may present three key disadvantages. First,the elements may operate in a very narrow band of wavelengths, and thussystems based on diffractive elements may require three waveguides, witheach waveguide individually processing one of the RGB wavelengths thusadding to the size and cost of the display system. Second, diffractiveelements display high angular selectivity, which may limit the range ofray angles directed by the grating towards the user, thus significantlylimiting the FOV achieved by the display. Third, many of the diffractiveelements currently in use have complex shapes that may require lengthyand/or costly manufacturing processes. Differences in the use andimplementation of the optical elements drive the differences inperformance achieved by existing display offerings.

Many development-level systems currently exist in the market thatattempt to harness and deliver the potential of AR, however such systemssuffer from a number of issues that limit their potential and/oreffectiveness for long term wearing and broad spectrum adoption. Forexample, existing systems may limit the field of view (FOV) presented toa user. The human eyes capture images from angles over 180 degreeshorizontally and 60 degrees vertically. Current optical systems used topresent three-dimensional (3D) images to a user's eyes may restrict thefield of view (FOV) to 30 degrees by 17 degrees. This limitation maydecrease the amount of information the system is able to present to theuser in a single frame. The following prior art system provide anoverview of those seen typically within the industry.

The BAE System having a principle place of business in Farnborough,United Kingdom, manufacturers the Quantum Display. The Quantum Displaygenerally utilizes a set of diffraction gratings expanding the exitpupil and generating a range of output ray angles. The display positionsthe image projector at a specific angle with respect to a horizontalwaveguide in order to accommodate for the angular selectivity of thediffraction gratings. The optics and mechanics required to achieve theoptimal launch conditions add significantly to the size and weight ofthe display, Light propagating through the first waveguide interactswith a diffraction grating placed or etched on the top surface, and thegrating diffracts a portion of the light into a vertical waveguide ateach point along horizontal waveguide. A second grating on the surfaceof the vertical waveguide performs a similar function, coupling lightout at each point of the waveguide surface at a range of anglesdetermined by the design of the diffraction grating. The current designprojects a collimated output beam and thus produces an output atinfinity, and does not provide for any accommodation allowance. Thedisplay produces a 30° FOV for one eye (monocular) and uses only one setof waveguides and gratings, limiting current versions to monochromeimage generation. The angular positioning of the source and therelatively large thickness of the waveguide make expanding the system tobinocular, RGB image generation impractical.

The Lumus display, as described in patent applications filed by Lumus(U.S. Pat. No., 7,391,573, U.S. Ser. No. 12/596,823 and U.S. Ser. No.12/092,818, for example), generally utilizes a set of reflectivesurfaces to perform in-coupling, expand the exit pupil and generate arange of output angles. The reflective surfaces rely on the reflectionand transmission of light at the boundary between two materials ofdifferent refractive index. Each reflector in the waveguide uses amulti-layer coating to produce a partially reflecting mirror. Light raysstriking the mirror at certain angles are partially reflected, sendinglight toward the user's eyes. An element design may prevent reflectionfrom the back of the element, which would send light out the side orrear of the waveguide, away from the user's eye. Several elementsdistributed along the length of the waveguide couple light out from anextended length along the horizontal direction, effectively expandingthe exit pupil in this direction. A similar optical element at thewaveguide input couples light into the waveguide from an imagegenerator. A series of lenses, mirrors, and prisms conditions andconverges the light from the image generator to coupling and create thedivergent beam to present a virtual image to the user. An additionaloptic may distribute light in the vertical direction to increase theexit pupil in the vertical direction as well as the horizontaldirection.

The Lumus display exhibits many design challenges that may limiteffectiveness. First, the in-coupling system requires custom, heavy, andbulky optics and a 45° angle, adding weight, size and cost to thesystem. Second, the eye pupil expansion in both the vertical andhorizontal direction may occur relatively slowly, requiring the beam totravel a long distance within the waveguide (around half an inch) beforereaching the out-coupling reflective elements. As a result, only a smallfraction (around ⅓^(rd)) of the glass area in front of the user's eyemay contribute to the production of an image, creating significant deadspace in the display. Since most of the FOV produced by a displaydepends on the size of the emitting area, the small image-producing areagreatly restricts the FOV to below 30 degrees. Third, the in-couplingoptical design may need to compensate for the polarization-dependentnature of the reflective out-coupling elements. To ensure that eachpolarization state reflects the same amount of power at each mirror, thein-coupling system may need to carefully control the angle at which eachstate enters the waveguide. The solution used in the Lumus displaycontributes to the size, weight and cost of the system.

Fourth, the display produces virtual images at a fixed accommodation andprovides no method for adjusting the accommodation to address thevergence-accommodation conflict. In natural viewing, a user's eyesadjust to objects at different distance by changing the focus of thelens (accommodation) to produce a clear image on the user's retina, andby rotating the eyes inward or outward such that the line of sight fromthe two eyes may converge at the same distance as the object (vergence).The Lumus display presents images at a fixed distance from the eyes suchthat the images create a virtual object at a perceived distance from theviewer. The eyes may rotate to adapt the vergence based on perceiveddepth, but the eyes remain focused on the screens, causing an unnaturaldisconnect between the vergence and accommodation activities. Thisdisconnect may cause moderate to severe problems for a user, includingeye strain, headaches and discomfort or disorientation. Further, suchissues may worsen over extended viewing periods.

Lastly, the current design of the reflective layers of the Lumus displayproduces scattering, which may reduce image clarity and/or may increasepower required to produce an image. Increased power requirements maystrain the limited battery capacity, limiting use time.

The Hololens system is manufactured by Microsoft, having a principleplace of business in Redmond, Wash., and utilizes a series ofspecialized diffractive gratings to perform in-coupling, exit pupilexpansion, and out-coupling. Generally, light from the image generatormay enter perpendicular to the waveguide and couple into the waveguideat specific angles through a specially designed diffraction grating. TheHololens system is further described in the article “Diffractive opticsfor virtual reality displays,” Journal of the Society for InformationDisplay, Vol. 14, No, 5, pp. 467-475, 2006, and is herein incorporatedby reference in its entirety. The grating possesses a tilted structurethat couples light in the outward direction toward the eye, with littleor no power directed away from the eye. An extended, cone-shaped gratingpanel uses a similar grating structure to expand the exit pupil in thehorizontal direction, directing fractions of light to the largergrating, which expands the exit pupil in the vertical direction. Thearea of the larger grating may effectively define the Hololens' exitpupil. The modulation depth of both gratings increases with distancefrom the in-coupling point such that the same amount of power reflectsfrom each point of the grating to produce a uniform intensity image. Aliquid crystal display contained in a separate layer provides selectiveocclusion of the external scene to improve image contrast.

The Hololens design presents many design challenges and choices that maylimit the system effectiveness and commercial viability. First, thedesign of the diffraction gratings makes the gratings exceedinglydifficult and quite costly to manufacture. Second, the diffractiongratings operate efficiently at only a single wavelength. To project RGBimages, the display uses three parallel waveguides, one for each color,with alignment carefully controlled to match pixel positions in eachwaveguide. Each eye therefore may require nine of the costly andcomplicated gratings, for a total of 18 gratings, quickly driving thecost of the system out of the range of most potential users. The use ofmultiple layers also increases the size and weight of the display,particularly at the front. Third, difficulties in producing the gratingsmay also limit the maximum area of the out-coupling grating and thus maylimit the FOV. The Hololens achieves a FOV of 30 degree horizontally and17 degrees vertically resulting in a restricted virtual world for theuser. Such a small FOV restrict the user's ability to work with multipleobjects simultaneously and/or view an entirety of a virtual scene (e.g.,objects on edge of scene may disappear or cut-off). Because of thelimited FOV, the user can typically see only one complete object at atime, with other objects out of view or only party visible, contrary tothe wide FOV concept pictures presented on the Hololens web page. Inorder to view a complete scene, a user may be required to turn theirhead and center each object within the FOV, causing other objects todisappear and/or placing motion strain on a user's neck. Lastly, thefixed nature and angular selectivity of the gratings precludes addingoptical components that would adjust beam divergence to alleviate thevergence-accommodation conflict.

The optical display manufactured by Magic Leap, having a principle placeof business in Plantation, Fla., and described in U.S. Pat. No.8,950,867, “Three Dimensional Virtual Augmented Reality Display System,”and U.S. Pat. No. 9,310,559, “Multiple Depth Plane Three-dimensionalDisplay Using a Waveguide Reflector Array Projector,” utilizes acombination of beam-splitters and micro-reflectors to produce the onlyprior art display attempting to address the accommodation-vergenceconflict. Generally, light couples from the image generator into acoupling tube, with the coupling process using a fiber or diffractiveelement, depending on the specific implementation. The coupling tube maycontain a series of beam splitters that reflect a portion of the lightinto an array of waveguide tubes. The coupling tube may expand the exitpupil in the vertical directions. Each waveguide tube contains a seriesof curved reflective elements that serve to expand the exit pupil in thehorizontal direction (similar to the Lumus display described herein) andto produce a specific divergence in the beam that may cause the virtualimage to appear at a specific distance from the user. To produce imagesat varying distances, multiple coupling-waveguide tube combinations maybe stacked in parallel with each combination containing reflectiveelements of different curvature. The total system may produce images attwelve discrete distances, and the system may produce a distancecontinuum by illuminating adjacent combinations with different opticalpower ratios. Switches or other elements select the amount of powerdelivered to each layer in the overall stack.

The Magic Leap design presents a number of challenging design issuesthat has prevented the completion of a working prototype. First, thestacked layers of coupling-waveguide tube combinations prove challengingand quite difficult and costly to produce. One such stack may requiremanufacturing of multiple tubes, each with multiple reflective elements,and each layer of tubes requiring a different curvature for thereflective elements. Second, the size of one such stack, coupled withthe need to produce a separate stack for each color to produce an RGBimage, may cause the size and weight of the display to grow rapidly. Thethickness of the display may exceed that of either the Hololens or Lumusdisplays. Third, little information exists on the method forimplementing layer selection and distribution of power amongst thelayers, leaving a number of design challenges unsolved based on thepresent information available. Fourth, light from one layer must passthrough one or more other layers as the light travels to the eye, whichraises the possibility of cross-talk and scattering issues that maylikely degrade image quality.

As such, there exists a need within the art for a low cost, lightweightand broad FOV optical display system to realize the potential of ARand/or VR systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments of the present disclosure are hereby illustrated inthe appended drawings. It is to be noted however, that the appendeddrawings only illustrate several typical embodiments and are thereforenot intended to be considered limiting of the scope of the presentdisclosure. Further, in the appended drawings, like or identicalreference numerals or letters may be used to identify common or similarelements, and not all such elements may be so numbered. The figures arenot necessarily to scale, and certain features and certain views of thefigures may be shown as exaggerated in scale or in schematic in theinterest of clarity and conciseness. Various dimensions shown in thefigures are not limited to those shown therein and are only intended tobe exemplary.

FIG. 1 is block diagram of an exemplary optical display system of thepresent disclosure.

FIGS. 2A, 2B and 2C are perspective views of exemplary optical displaysystems of the present disclosure.

FIG. 3 is a block diagram of an exemplary diffraction enhanced opticalimaging system for use in the optical display system illustrated in FIG.1.

FIG. 4 is a graphical representation of example output of an exemplaryembodiment of the diffraction enhanced optical imaging systemillustrated in FIG. 3.

FIG. 5 is a block diagram of another exemplary diffraction enhancedoptical imaging system for use in the optical display system illustratedin FIG. 1.

FIG. 6 is a graphical representation of example output of an exemplaryembodiment of the diffraction enhanced optical imaging systemillustrated in FIG. 5.

FIG. 7A is a block diagram of another exemplary diffraction enhancedoptical imaging system for use in the optical display system illustratedin FIG. 1.

FIG. 7B is a block diagram of another exemplary diffraction enhancedoptical imaging system for use in the optical display system illustratedin FIG. 1.

FIG. 8A is a block diagram of an exemplary in-coupling diffractionelement for use in the optical display system illustrated in FIG. 1.

FIG. 8B is a graphical representation of example output of an exemplaryembodiment of the in-coupling diffraction element illustrated in FIG. 8.

FIGS. 9A and 9B are block diagrams of exemplary in-coupling diffractionelements for use in the optical display system illustrated in FIG. 1.

FIG. 10 is a block diagram of an exemplary wavelength compensated beamexpander for use in the optical display system illustrated in FIG. 1.

FIGS. 11A-11C are block diagrams of exemplary optical elements for usein the wavelength compensated beam expander illustrated in FIG. 10.

FIG. 12 is a graphical representation of example output of an exemplaryembodiment of the wavelength compensated beam expander illustrated inFIG. 10.

FIG. 13 is a block diagram of an exemplary output coupling and verticalexpansion system for use in the optical display system illustrated inFIG. 1.

FIGS. 14 and 15 are graphical representation of example output of anexemplary embodiment of the output coupling and vertical expansionsystem illustrated in FIG. 13.

DETAILED DESCRIPTION

The present disclosure describes an optical display system for use inaugmented reality systems and/or virtual reality systems. Generally, theoptical display system may maximize coupling of light from an imagegenerator to an optical waveguide, include image magnification (e.g.,exit pupil expansion) and wavelength dispersion correction over shortdistances to minimize size and/or weight of the optical display system,out-couple light substantially equally at most or all wavelengths over asignificant area and range of angles to achieve a field of view (FOV)greater than 30 degrees, greater than 40 degrees, greater than 50degrees, greater than 60 degrees, and/or provide beam divergence toprovide natural eye accommodation. In some embodiments, the opticaldisplay system may include electrical and/or software components fordriving image generators.

In some embodiments, the optical display system may providethree-dimensional, two-dimensional, convergence corrected, and/orfull-color images to a user while minimizing size and/or weight of theoptical display system. In some embodiments, the optical display systemmay use only a single waveguide to expand and/or direct light from animage generator to a user's eyes. A combination of diffractive elementsmay provide beam expansion within short distances and/or correction ofchromatic aberrations within the optical display system to provide asharp image with a wide FOV. Output couplers may provide additionalenhancement of the FOV in some embodiments. A variable optical elementmay change divergence of the beam that reaches the output couplers,allowing the optical display system to change perceived distance of anobject from the user and provide substantially correct convergence toensure natural viewing by the user. A refractive optical element mayprovide images at different angles from an optical axis, as well asdifferent distances from an output plane of the lens. A multi-layerdiffractive optical element may provide wavelength dispersion ofopposite sign.

Before describing various embodiments of the present disclosure in moredetail by way of exemplary descriptions, examples, and results, it is tobe understood that the embodiments of the present disclosure are notlimited in application to the details of systems, methods, andcompositions as set forth in the following description. The embodimentsof the present disclosure are capable of other embodiments or of beingpracticed or carried out in various ways. As such, the language usedherein is intended to be given the broadest possible scope and meaning;and the embodiments are meant to be exemplary, not exhaustive. Also, itis to be understood that the phraseology and terminology employed hereinis for the purpose of description and should not be regarded as limitingunless otherwise indicated as so. Moreover, in the following detaileddescription, numerous specific details are set forth in order to providea more thorough understanding of the disclosure. However, it will beapparent to a person having ordinary skill in the art that theembodiments of the present disclosure may be practiced without thesespecific details. In other instances, features that are well known topersons of ordinary skill in the art have not been described in detailto avoid unnecessary complication of the description.

Unless otherwise defined herein, scientific and technical terms used inconnection with the embodiments of the present disclosure shall have themeanings that are commonly understood by those having ordinary skill inthe art. Further, unless otherwise required by context, singular termsshall include pluralities and plural terms shall include the singular.

All patents, published patent applications, and non-patent publicationsreferenced in any portion of this application are herein expresslyincorporated by reference in their entirety to the same extent as ifeach individual patent or publication was specifically and individuallyindicated to be incorporated by reference.

As utilized in accordance with the concepts of the present disclosure,the following terms, unless otherwise indicated, shall be understood tohave the following meanings:

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one,” butit is also consistent with the meaning of “one or more,” “at least one,”and “one or more than one.” The use of the term “or” in the claimsand/or the specification is used to mean “and/or” unless explicitlyindicated to refer to alternatives only or when the alternatives aremutually exclusive, although the disclosure supports a definition thatrefers to only alternatives and “and/or.” The use of the term “at leastone” will be understood to include one as well as any quantity more thanone, including but not limited to 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20,30, 40, 50, 100, or any integer inclusive therein. The term “at leastone” may extend up to 100 or 1000 or more, depending on the term towhich it is attached; in addition, the quantities of 100/1000 are not tobe considered limiting, as higher limits may also produce satisfactoryresults. In addition, the use of the term “at least one of X, Y and Z”will be understood to include X alone, Y alone, and Z alone, as well asany combination of X, Y, and Z.

As used in this specification and claim(s), the words “comprising” (andany form of comprising, such as “comprise” and “comprises”), “having”(and any form of having, such as “have” and “has”), “including” (and anyform of including, such as “includes” and “include”) or “containing”(and any form of containing, such as “contains” and “contain”) areinclusive or open-ended and do not exclude additional, unrecitedelements or method steps.

The term “or combinations thereof” as used herein refers to allpermutations and combinations of the listed items preceding the term.For example, “A, B, C, or combinations thereof” is intended to includeat least one of: A, B, C, AB, AC, BC, or ABC, and if order is importantin a particular context, also BA, CA, CB, CBA, BCA, AGB, BAC, or CAB.Continuing with this example, expressly included are combinations thatcontain repeats of one or more item or term, such as BB, AAA, AAB, BBC,AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan willunderstand that typically there is no limit on the number of items orterms in any combination, unless otherwise apparent from the context.

Throughout this application, the term “about” is used to indicate that avalue includes the inherent variation of error that exists among thestudy subjects. Further, in this detailed description, each numericalvalue (e.g., temperature or time) should be read once as modified by theterm “about” (unless already expressly so modified), and then read againas not so modified unless otherwise indicated in context. Also, anyrange listed or described herein is intended to include, implicitly orexplicitly, any number within the range, particularly all integers,including the end points, and is to be considered as having been sostated. For example, “a range from 1 to 10” is to be read as indicatingeach possible number, particularly integers, along the continuum betweenabout 1 and about 10. Thus, even if specific data points within therange, or even no data points within the range, are explicitlyidentified or specifically referred to, it is to be understood that anydata points within the range are to be considered to have beenspecified, and that the inventors possessed knowledge of the entirerange and the points within the range. Further, an embodiment having afeature characterized by the range does not have to be achieved forevery value in the range, but can be achieved for just a subset of therange. For example, where a range covers units 1-10, the featurespecified by the range could be achieved for only units 4-6 in aparticular embodiment.

As used herein, the term “substantially” means that the subsequentlydescribed event or circumstance completely occurs or that thesubsequently described event or circumstance occurs to a great extent ordegree. For example, the term “substantially” means that thesubsequently described event or circumstance occurs at least 90% of thetime, or at least 95% of the time, or at least 98% of the time.

Referring to the Figures, and in particular to FIGS. 1 and 2A-2B,illustrated are optical display systems 10 for providingthree-dimensional, two-dimensional, convergence corrected images to auser. Images may be full-color images, limited color images, grayscaleimages, and/or black and white images. Generally, the optical displaysystem 10 may couple one or more images into an optical waveguide 12. Itshould be noted that images may include still images, video, animation,and/or the like. Additionally, the optical display system 10 may beconfigured to magnify the image in a horizontal direction and/orhorizontal and vertical directions without producing any or minimalwavelength separation and/or distortion of the one or more images. Tothat end, the optical display system 10 may include one or morediffraction enhanced imaging systems 16 configured to collect one ormore rays 18 produced by the image generator 14 (e.g., DLP projector,LCD display system, LCOS display system, GLV system, fiber controlleddisplay system, and/or the like). The diffraction enhanced imagingsystem 16 may control convergence angle of each of the rays 18 at eachwavelength (e.g., red, green, blue) prior to coupling each of the rays18 into the optical waveguide 12. One or more in-coupling diffractionsystems 20 may use diffraction to couple the incoming rays 18 into theoptical waveguide 12 at specific convergence and/or divergence anglesneeded by subsequent systems to produce an expanded beam having specificfinal divergence angles. Within the optical waveguide 12, one or morewavelength compensated beam expanders 22 configured to simultaneouslyexpand horizontal extension of the image (i.e., horizontalmagnification), and/or compensate for wavelength dispersion such thatcolor components of each image pixel may overlap precisely at one ormore output coupling and vertical expansion systems 24. The outputcoupling and vertical expansion system 24 may be configured to magnifythe image in a vertical direction and/or to direct a fraction of lighttowards the user at specific angles to create a wide FOV. It should benoted that via rotation of the optical display system 10, horizontalmovement may become vertical and vertical movement may becomehorizontal. FIG. 2C illustrates an exemplary vertical arrangement of theoptical display system 10.

In some embodiments, an adjustable optical element may be configured tocontrol apparent distance at which the object appears such that theeye's convergence and accommodation system may work in concert,resulting in reduced fatigue and disorientation. One or more of thewavelength compensated beam expanders 22 may contain adjustablecomponents that maintain the overlap of the color components of eachimage pixel for different configurations of the adjustable opticalelement. Other systems, as described herein, may control and/orcoordinate generation of one or more images, track user movement (e.g.,determine user directed attention), track user's eyes movement, mapexternal surrounding, and/or the like.

Details and possible embodiments of the optical display system 10 andeach of the diffraction enhanced imaging system(s) 16, in-couplingdiffraction system(s) 20, wavelength compensated beam expander(s) 22,and output coupling and vertical expansion system(s) 24 are hereindescribed.

In some embodiments, the optical display system 10 may be housed in aheadset 30 as illustrated in FIGS. 2A and 2B. The headset 30 may includea frame 32. In some embodiments, the frame 32 may include one or moreportions 34 configured to rest on a nose and/or ears of a user. In someembodiments, the frame 32 may include a band (not shown) configured tosecure the headset 30 to a user's head. For example, the band may be anelastic band configured to secure the headset 30 to the user's head. Insome embodiments, the frame 32 may be mounted within a helmet (notshown) configured to be positioned on a user's head.

Referring to FIGS. 2A and 2B, in some embodiments, the frame 32 mayinclude a front support element 36. Two or more image generators 14 maybe spatially disposed and positioned on the front support element 36.Each image generator 14 may be configured to provide a separate image toeach eye. For example, a first image generator 14 a may be configured toprovide a first image to a left eye of a user and a second imagegenerator 14 b may be configured to provide a second image to a righteye of the user. In FIG. 2A, the image generators 14 a and 14 b areillustrated as positioned adjacent to temples of a user on the frame 32.In FIG. 2B, the image generators 14 a and 14 b are illustrated aspositioned at the bridge of a nose of a user on the frame 32.

Referring to FIGS. 1 and 2A-2B, the diffraction enhanced imaging system16 includes a plurality of lens 38 (designated by way of example as 38 aand 38 b in FIG. 2A and 2B) positioned in the frame 32 with the lens 38a such that an image may be substantially aligned with one of the user'seyes and the lens 38 b such that an image may be substantially alignedwith the other one of the user's eyes. Generally, the lens 38 includesboth diffractive and refractive portions configured to alter wavelengthdispersion effects on the image distance produced by the lens 38.Referring to FIG. 3, the lens 38 may include multiple layers including,but not limited to, a first substrate layer 40, a first diffractivegrating layer 42, a spacer layer 44, a second diffractive grating layer46, and a second substrate layer 48.

The first substrate layer 40 may be formed of glass and/or otheroptically clear (e.g., transparent) material having known wavelengthdispersion properties. The first substrate layer 40 may include a firstsurface 50 and a second surface 52. The first surface 50 and/or thesecond surface 52 may be curved. Alternatively, the first surface 50and/or the second surface 52 may be substantially flat. In someembodiments, at least one of the first surface 50 and the second surface52 may be curved, such as, for example, the second surface 52 asillustrated in FIG. 3.

Referring to FIG. 3, the lens 38 may include the first diffractivegrating layer 42 positioned adjacent to the second surface 52 of thefirst substrate layer 40. The first diffractive grating layer 42 mayinclude at least one grating 54 formed of a holographic orsurface-contained periodic modulation of the optical refractive index orsurface height, respectively. In some embodiments, a bulk materialsubstantially similar in index and clarity with materiality of theoptical waveguide 12 may be used to write the gratings 54.

Period of the grating 54 of the first diffractive grating layer 42 mayimpact wavelength dispersion, both magnitude and sign, of the lightgenerated by the one or more imaging generators 14. Grating 54 may aidin a higher coupling efficiency as compared to other prior art couplingmethods. Higher coupling efficiency may translate into lower powerrequirements at input and/or brighter images presented to a user.

Referring to FIG. 3, the lens 38 may also include a spacer layer 44. Thespacer layer 44 may occupy space between the first diffractive gratinglayer 42 and the second diffractive grating layer 46. In someembodiments, the spacer layer 44 may be formed of optically clear (e.g.,transparent) material to light in the visible spectrum, for example. Insome embodiments, a portion or the entirety of the spacer layer 44 mayinclude air. The refractive index of the spacer layer 44 may impactdiffraction properties of the first diffractive grating layer 42 and/orthe second diffractive grating layer 46.

The second diffractive grating layer 46 may be positioned adjacent tothe spacer layer 44. In some embodiments, the second diffractive gratinglayer 46 may be formed of substantially similar material and propertiesas the first diffractive grating layer 42. The second diffractivegrating layer 46 may include at least one grating 56 formed of aholographic or surface-contained periodic modulation of the opticalrefractive index or surface height, respectively. Period of the grating56 of the second diffractive grating layer 46 may impact wavelengthdispersion, both magnitude and sign, of the light generated by theimaging generator 14. Generally, grating variation with position maycomplement variation of the first diffractive grating 42. For example,in a surface-etched grating, peaks of the grating 56 of the seconddiffractive grating layer 46 may lie at substantially the same positionas valleys of the grating 54 of the first diffractive grating layer 42.

The second substrate layer 48 may be positioned adjacent to the seconddiffractive grating layer 46. The second substrate layer 48 may beformed of glass and/or other optically clear material having knownwavelength dispersion. In some embodiments, dispersion magnitude and/orsign of the second substrate layer 48 may be different than dispersionmagnitude and/or sign of the first substrate layer 40. The secondsubstrate layer 48 may include a first surface 358 and a second surface60. The first surface 358 and/or the second surface 60 may be curved.Alternatively, the first surface 58 and/or the second surface 60 may besubstantially flat. In some embodiments, at least one of the firstsurface 53 and the second surface 60 may be curved, such as, forexample, the second surface 60 as illustrated in FIG. 3.

In some embodiments, at least one of the first substrate layer 40, firstdiffractive grating layer 42, spacer layer 44, second diffractivegrating layer 46, and second substrate layer 48 may consist of one ormore materials having a refractive index configured to be controlled byapplication of an electric field (e.g., via applied voltage). Changingthe refractive index of the material may alter either or both refractiveproperties and diffractive properties of the lens 38 thus altering imagedistances and/or corresponding convergence or divergence of rays exitingthe lens 38, FIG. 4 illistrates an example of a graph 70 of an exemplaryoutput of an exemplary embodiment of the lens 38. Generally, magnitudeof the difference in focal length between red wavelength 72, greenwavelength 74 and blue wavelength 76 may depend on wavelength dispersionof materials used in each layer of the lens 38. In the exemplaryembodiments illustrated in FIG. 4, a first material may have a change inrefractive index of 0.013364 between the red wavelength 72 and the bluewavelength 76, and a second material may have a refractive index changeof 0.027 between the red wavelength 72 and the blue wavelength 76.

In some embodiments, the lens 38 may further include a refractiveoptical element and/or wedge element 80 as illustrated in FIG. 5. Thewedge element 80 may be configured to provide images at different anglesfrom an optical axis 82, as well as different distances from an outputplane of the lens 38. The wedge element may be placed within the layersof the lens 38 as shown in FIG. 5, before lens 38 (between the imagegenerator 14 and the front layer 50 of first substrate 40), or afterlens 38 (beyond the second layer 60 of second substrate 48) and prior towaveguide 12. Referring to FIGS. 5 and 6, the wedge element 80 maycreate a 0.57 degree tilt in an imaging axis for blue wavelengths 76,but only a 0.548 degree tilt in the imaging axis for red wavelengths 72,for example, as shown in graph 84 illustrating output of the lens 38having the wedge element 80. The wedge angle ⊖_(W) may be determined toachieve a pre-determined angle in output rays and/or imaging axes. Insome embodiments, wedge angle ⊖_(W) may be determined and/or dependenton materiality of the wedge element 80, focal length of the lens 38,and/or focal power of the lens 38. In some embodiments, the wedge angle⊖_(W) may be up to 10 degrees, for example. As a result, light atdifferent wavelengths 72, 74 and 76 may enter the in-couplingdiffraction system 20 (shown in FIG. 1) at different angles and/ordifferent positions.

Referring to FIGS. 1 and 7A, in some embodiments, a second refractiveelement 86 may be positioned adjacent to but spaced a distance away fromthe lens 38. In some embodiments, the second refractive element 86 maybe a variable focal length lens configured to modify divergence of raysexiting the lens 38. The second refractive element 86 may be, forexample, a liquid-based variable focal length lens and/or otherrefractive element capable of modifying divergence of rays exiting thelens 38.

Referring to FIGS. 1 and 7B, in some embodiments, a refractive element88 may be positioned adjacent to and in contact with the lens 38. Therefractive element 88 may be, for example, one or more lens formed ofdispersive material to counteract and/or enhance wavelength dispersionof the lens 38 to increase or decrease wavelength dispersion of theoptical display system 10. In some embodiments, the refractive element88 may be formed of material having a refractive index more stronglydependent on wavelength than standard optical glasses (e.g., BK7), inthat the material has a greater change in refractive index as a functionof wavelength than standard glasses, for example.

Referring to FIGS. 1 and 8A, the in-coupling diffraction system 20redirects light incident on the diffraction enhanced imaging system 16into a different direction of travel such that light may propagate in aguided way along a length of the optical waveguide 12. In someembodiments, the in-coupling diffraction system 20 may include a singlediffraction grating 90. Using the single diffraction grating 90 mayfurther reduce size of the in-coupling diffraction system 20 and reducemanufacturing and complexity cost. Period of the single diffractiongrating 90 may be selected such that rays entering the singlediffraction grating 90 from the diffraction enhanced imaging system 16exit the single diffraction grating 90 at angles conducive topropagation within the optical waveguide 12 by total internal reflection(TIR). Period of the single diffraction grating 90 may also alter raycone for each wavelength to create a new image point, either virtual orreal, that may act as an input image for the wavelength compensated beamexpander 22 (shown in FIG. 1).

Gratings 92 in the single diffraction grating 90 may affect lightentering normal to the optical waveguide 12, simplifying and/orminimizing size of optics between the image generator 14 and the opticalwaveguide 12. In some embodiments, period of the single diffractiongrating 90 may be selected to modify (i.e., enhance or reduce)wavelength dispersion introduced by the diffraction enhanced imagingsystem 16. The single diffraction grating 90 may contain blazing and/orother design configured to couple energy into forward propagatingdirection (i.e., either positive 1^(st) order or negative 1^(st) orderdiffraction) minimizing loss of optical power during coupling. Blazingis altering symmetry of each period of the grating 92 to supportconstructive interference in one direction and/or angle out of thegrating 92 and/or create strong destructive interference in other anglesat which the grating 92 may attempt to diffract light. Depth and lengthof the grating 92 may also influence coupling efficiency, and may beselected to maximize power coupled into desired diffraction orderwithout making grating complicated or costly to manufacture. Thegratings 92 may consist of either a holographic (index-based) grating,alternating materials of different refractive index in a periodic mannerover distance, dynamic diffractive elements, subwavelength diffractiveelements, and/or an amplitude grating (periodic surface structure).

For the structure of the gratings 92, parameters may include modulationperiod (∧∧_(g)), depth of modulation, and shape of function within eachmodulation period. Referring to FIG. 8A, illustrated therein is lightpassing through the single diffraction grating 90 having gratings 92.Some portion of the light does not diffract (m=0 or 0^(th) order), andfractions of the optical power diffract primarily into two first orderbeams (m=±1), each exiting at angle ⊖_(d) that depends on ∧∧_(g) andwavelength λ, according to the equation:

$\begin{matrix}{\theta_{d} = {\sin^{- 1}\left( {\frac{m\;\lambda}{\Lambda_{g}} + {\sin\left( \theta_{in} \right)}} \right)}} & \left( {{EQ}.\mspace{14mu} 1} \right)\end{matrix}$

wherein ⊖_(in) is the angle of the incoming light with respect to thegrating normal, which equals zero for base design of the optical displaysystem 10. A greater depth of modulation generally increases thecoupling efficiency which determines the fraction of incident powerdirected into first-order beams. Functional shape within each period ofthe gratings 92 may also influence diffraction efficiency for twofirst-order beams. A sinusoidal shape couples power equally into firstorder beams. As illustrated in FIG. 8A, power entering the −1 order maynot travel to the user's eye, and thus may represent a loss in theoptical display system 10. Altering shape of variation, includingblazing, from sinusoidal to some other shape may diffract power into the+1 order and significantly weaken coupling into the −1 order, increasingpower delivered to the user's eye and increasing in-coupling efficiency.Length of grating 92 and positioning of the image generator 14 alonglength of the grating 92 may also influence diffraction efficiency.

FIG. 8B illustrates a graph 94 of a result of an exemplary embodiment ofthe in-coupling diffraction system 20 having a grating period of 1.648μm. Rays diffract away from the in-coupling diffraction system 20 indiffraction directions and at different divergences for each of thethree wavelengths.

Distance between the diffraction enhanced imaging system 16 and thein-coupling diffraction system 20 may be configured to aid inpropagation of the light. The distance may determine width of the beamof light for each color at the input plane of the in-couplingdiffraction system 20, and the difference in location of where thecenter of the beams intercept the in-coupling diffraction system 20. Insome embodiments, both beam width and beam axis location at the singlediffraction grating 90 may be selected such that the resulting beams oflight for each of the wavelengths have substantially similar width andbeam axis when exiting the wavelength compensated beam expander 22. Inthe exemplary embodiment illustrated in FIG. 8B, the single diffractiongrating 90 was positioned at a distance of 5.865 mm from the diffractionenhanced imaging system 16.

Referring to FIGS. 9A and 9B, in some embodiments, the in-couplingdiffraction system 20 may include multiple diffraction gratings 90 witheach grating tuned to one of the three RGB colors such that eachindependently controls imaging properties of each wavelength. In someembodiments, multiple gratings may include three spatially distinctdiffraction gratings 90 a, 90 b and 90 c as illustrated in FIG. 9A. Eachdiffraction grating 90 a, 90 b and 90 c may be layered one behind theother, with angular output of each grating chosen to compensate for thedifference in depth from which each output may be generated. In someembodiments, multiple gratings 90 a, 90 b and 90 c may be formed withinthe same material as illustrated in FIG. 9B. The gratings 90 a, 90 b and90 c may be superposed on one another, minimizing depth and/or thicknessof the in-coupling diffraction system 20 and subsequent opticalwaveguide 12. In some embodiments, each may include a sinusoidal patternhaving a different period and/or frequency.

Referring to FIGS. 1 and 10, images from the in-coupling diffractionsystem 20 may be propagated towards the wavelength compensated beamexpander 22. The wavelength compensated beam expander 22 may provide anoutput image that contains magnification in a horizontal directionand/or corrects for wavelength dispersion such that color components ofeach pixel spatially overlap. Within the optical waveguide 12, thewavelength compensated beam expander 22 may include one or more opticalelements 96 configured to simultaneously expand horizontal extension ofthe image (i.e., horizontal magnification), and/or compensate forwavelength dispersion such that color components of each image pixel mayoverlap precisely at one or more output coupling and vertical expansionsystems 24. Generally, diffracted light from in-coupling diffractionsystem 20 may strike each optical element 96 in series, with thedivergence and/or wavelength dispersion properties being altered at eachoptical element 96. In some embodiments, at least two of the opticalelements 96 may be configured as curved mirrors and/or the like. Theoptical elements 96 may alter the beam width based on relative focallengths of each optical element 96 and/or distance traveled between eachoptical element 96.

The wavelength compensated beam expander 22 receives images formed bythe in-coupling diffractive system 20 at each wavelength. Light from theimage may either directly illuminate a first optical element 96a orilluminate the first optical element 96 a after one or more reflectionswithin the optical waveguide 12, depending on design of the firstoptical element 96 a and/or needs of the application. The first opticalelement 96 a may produce a subsequent image, one for each wavelength,via diffraction and/or reflection, and may provide corrective action toreduce wavelength dispersion introduced by the diffraction enhancedimaging system 16 and the in-coupling diffractive system 20. The imageproduced by the first optical element 96 a may act as the input to thesecond optical element 96 b. Light from the image produced by the firstoptical element 96 a may either directly illuminate the second opticalelement 96 b or may illuminate the second optical element 96 b after oneor more reflections within the optical waveguide 12. The design of thesecond optical element 96 b may produce images at infinity (i.e.,collimated light) for each wavelength under initial design conditions,with the position and propagation direction (i.e., angle) of each outputbeam overlapping and coinciding with that of the beams for the otherwavelengths.

For both the first optical element 96 a and the second optical element96 b, thickness of the optical waveguide 12 may determine the effectiveobject distances for the elements. Distance of the object combined withdesign of each optical element 96 a and 96 b may determine the distanceof the image for each wavelength. Further, selection of thickness forthe optical waveguide 12 may allow for objects and images to appear atdistances in concert with diffractive nature of the first opticalelement 96 a and the second optical element 96 b to provide correctedfinal output properties for each of the wavelengths. Additional opticalelements (e.g., 96 c. . . 96 n) may be used within the beam expander 22and the output coupling and vertical expansion system 24.

Imaging properties of each optical element 96 may depend on effectiveshape of the optical element 96. For example, spherical shapes mayproduce greater distortion as compared to aspheric shapes. In someembodiments, an intermediate image may be produced between two opticalelements 96. Depending on design, each optical element 96 may reduce orincrease a difference in ray angles between wavelengths that occur dueto in-coupling grating (e.g., wavelength dispersion). To minimize and/oreliminate wavelength dispersion and/or maximize image clarity, anadditional optical element 96 (e.g., 96 c. . . 96 n) may be used withinthe beam expander 22. Such additional optical element 96 may beconfigured to compensate and/or correct for differences in ray anglesamong wavelengths. As such, beam expander 22 may produce a large lateralmagnification in a short distance, provide a collimated output beam,and/or minimize wavelength dispersion artifacts in the image.

Each optical element 96 may include at least one of a reflective mirror98, a single-axis Fresnel reflector 100, and a reflection grating 102.

Referring to FIG. 11A, the reflective mirror 98 may include a firstsurface 104. In some embodiments, the first surface 104 may be a curvedsurface. For example, the first surface 104 may be spherical, aspheric,and/or the like. In some embodiments, curvature of the first surface 104may be dependent on function of the optical element 96. The reflectivemirror 98 may include a first end 106 and a second end 108. In someembodiments, the first end 106 and/or the second end 108 may betruncated such that a vertex is offset from center C of the reflectivemirror 98. With the vertex offset from center C, output angles may beadjusted for the reflected beam. Width w and length I of the reflectivemirror 98 may be sufficient to intercept all or substantially allincoming light rays to minimize optical loss at the optical element 96.

Referring to FIG. 11B, the single-axis Fresnel reflector 100 may embodythe concept of Fresnel zones to provide imaging along only one axisand/or direction. Fresnel reflectors 100 create effects of a curvedsurface by slicing the surface into rings (two-dimensional) or strips(one-dimensional) and placing such rings or strips in a flat plane. Theone-dimensional configuration may alter beam width along only one axis.Constructive and destructive interference between light rays reflectedfrom each strip may effectively focus or defocus optical power in theincident beam.

Size of each Fresnel zone 110 in the Fresnel reflector 100 may bedetermined by effective focal length for the optical element 96 and/orwavelength for which desired effective focal length may be achieved.Center of each Fresnel zone 110 of the Fresnel reflector 100 may bedetermined using the following equation:

$\begin{matrix}{r_{n} = \sqrt{{n\;\lambda\; f} + \frac{n^{2}\lambda^{2}}{4}}} & \left( {{EQ}.\mspace{14mu} 2} \right)\end{matrix}$

wherein r_(n) is the distance from the center of the Fresnel reflector100 to the center of the n^(th) Fresnel zone, n is a positive integer, fis the desired focal length of the Fresnel reflector 100, and λ is thedesign wavelength. The design wavelength may be selected to achievespecific values of wavelength dispersion (e.g., variation in value of fas a function of wavelength) to counteract, in part or in whole,dispersion generated by the diffraction enhanced imaging system 16 andthe in-coupling diffractive system 20. Width and length of the opticalelement 96 may be sufficient to intercept all incoming light rays inorder to minimize optical loss at the optical element 96. The Fresnelreflector 100 may be constructed with the n=0 zone positioned less thanhalfway between a first edge 112 and a second edge 114 of the Fresnelreflector 100. Such positioning may obtain one or more desired outputangles for reflected beams by having light from each wavelength strikethe Fresnel reflector 100 at different positions, and as such, differenteffective curvature thus changing the direction of the 0^(th) orderreflection.

Referring to FIG. 11C, in some embodiments, the optical element 96 mayinclude the reflection grating 102. The angle of reflection from thereflection grating 102 may be dependent on gratings 116 causing areflected angle in a nonlinear manner, and as such, may alterdivergence/convergence point of a cone of rays effectively changinglocation of the image with respect to the next optical element (e.g., 96b). The change in location of the image may depend on the wavelength,and as such, the reflective grating 116 may alter and/or compensate forwavelength dispersion. Other factors influencing reflection angle mayinclude, but are not limited to, period of the grating, use of blazingto diffract light into a specific diffraction order, and/or the like.

In some embodiments, the optical element 96 may be positioned on theexterior of the optical waveguide 12 as illustrated in FIG. 10. Lightmay pass through the optical waveguide 12 to the optical element 96. Insome embodiments, space between the optical waveguide 12 and the opticalelement 96 may be filled with an optically clear material. Therefractive index of the material maybe selected to reduce and/oreliminate total internal reflection at the wall of the optical waveguide12 and/or minimize bending of rays passing through the optical waveguide12 to the optical element 96. In some embodiments, the refractive indexof the optically clear material may be substantially similar (a percentdifference of less than 5%, for example) to the refractive index of theoptical waveguide 12. In some embodiments, the material of the opticallyclear material may be an optical epoxy. In some embodiments, thematerial of the optically clear material may include adhesive propertiessuch that the optical element 96 may be attached to the opticalwaveguide 12. In some embodiments, the optical element 96 may beattached using a separate adhesive material and/or structure.

In some embodiments, the space between optical waveguide 12 and theoptical element 96 may be filled with a material possessing a refractiveindex controllable by an applied electric field. Applying an electricfield, including but not limited to an applied voltage or current, mayraise or lower the refractive index, depending on the properties of thematerial and polarity of the applied electric field. Raising or loweringthe refractive index makes the refractive index of the materialdifferent from that of the optical waveguide 12, causing refractivebending of the light rays at the boundary between the material and theoptical waveguide 12. Refractive bending may change the effectivelocation and/or distance of the object for the optical element 96,thereby changing the imaging properties (divergence, image location andtype) of the optical element 96 and thus changing the wavelengthdispersion compensation achieved by the optical element 96. The changein wavelength dispersion compensation may allow the wavelengthcompensated beam expander 22 to correct for changes in the wavelengthdispersion of the diffraction enhanced imaging system 16 resulting fromchanges in the second refractive element 86.

In some embodiments, a piezo electric material may be positioned as aspacer between the wall of waveguide 12 and the optical element 96. Avoltage applied to the piezo electric material may cause the piezoelectric material to expand or contract in size, subsequently causingthe optical element 96 to move closer to or further away from wall ofwaveguide 12. In some embodiments, two or more piezo electric spacersmay be used to change the tilt of the optical element 96. For example,the piezo electric spacer on one side may be directed to expand whilethe piezo electric spacer on the opposite side may be directed tocontract, causing the optical element 96 to obtain a tilt with respectto the wall of waveguide 12, with the tilt oriented toward the side onwhich the piezo electric spacer expanded and oriented away from the sideon which the piezo electric spacer contracted. The change in distancebetween optical element 96 and the wall of waveguide 12 may change theeffective object distance between the prior image and the opticalelement 96, thereby changing the imaging properties (divergence, imagelocation and type) of the optical element 96 and thus changing thewavelength dispersion compensation achieved by the optical element 96.The change in wavelength dispersion compensation may allow thewavelength compensated beam expander 22 to correct for changes in thewavelength dispersion of the diffraction enhanced imaging system 16resulting from changes in the second refractive element 86.

In some embodiments, the optical element 96 may be formed within thewall of the optical waveguide 12. For example, in some embodiments, thewall of the optical waveguide 12 may be sculpted to a desired shape. Theexterior surface of the optical waveguide 12 may then be coated with areflective coating forming the optical element 96. The reflectivecoating may consist of a metal substance, for example, reflecting ateach of the RGB wavelengths. Other coatings and/or implementation of thereflective coating, such as dielectric coatings, are contemplated thatprovide for equal reflection power at each of the RGB wavelengths.

FIG. 12 illustrates a graph 120 of output for an exemplary wavelengthcompensated beam expander 22 having at least one optical element 96including the single axis Fresnel reflector 100. The single axis Fresnelreflector 100 may collect light and bring reflections to a focal pointwith the optical waveguide 12. In this example, the first opticalelement 96 a has a focal length of 0.14 mm at a design wavelength of 665nm, and the center of the first optical element 96 a is positioned 2.2μm from the central axis of the red wavelength 72. Other combination ofthickness for the optical waveguide 12, focal length, design wavelength,and reflector center may potentially produce equal width beams at thesecond optical element 96 b. Each wavelength may focus at a differentdistance and/or angle within the optical waveguide 12, and the width ofbeam at the input plane of the second optical element 96 b (e.g., secondsingle-axis Fresnel reflector 100) may be substantially equal for allwavelengths. The second optical element 96 b may utilize a designproviding collimated light at substantially all wavelengths anddirection of wavelengths down the length at substantially the sameangle. In some embodiments, small focal length (e.g., less than or equalto 0.1 mm), may be utilized and/or reflection from at least a section ofthe second optical element 96 b off-center may be used. Off-centeredreflection may provide less divergence in output beams, with less than0.005 degrees of divergence shown in FIG. 12. The output angle providedmay also produce total-internal reflection of all wavelengths about thewalls of the optical waveguide 12.

Referring to FIGS. 1 and 13, the output coupling and vertical expansionsystem 24 may magnify the image in a vertical direction creating a largeoutput area (i.e., exit pupil). The output coupling and verticalexpansion system 24 may include a vertically oriented waveguide 122employing a vertical beam expanding element 121 and two or morereflecting elements 124 configured to magnify the exit pupil in avertical direction and/or to direct a fraction of light out of thevertically oriented waveguide 122 and towards the user at specificangles to create a wide FOV. A large exit pupil, combined with the rangeof light angles entering the eye may produce the large total FOV. TheFOV describes the range of angles over which the user may perceive theimage generated by the optical display system 10, and may determine thesize of viewing area for the user. A larger FOV may allow the user toobserve scenes and objects over a larger range, reducing the need toturn the user's head to view images away from a center of vision and/orpreventing objects from clipping or disappearing off edges of the imageswhen looking at another object. After the image expands and propagatesalong the optical waveguide 12, a turning optic 126 may direct the imagein a vertical direction as shown in FIG. 13. The turning optic 126 mayconsist of, but is not limited to, a mirrored surface, consisting of oneor more discrete component surfaces deflecting light, or a distributedreflecting element, including but not limited to a long-period variationin the refractive index for which reflection rather than diffraction maybe the predominant optical effect Fabry Perot Filters, and/or the like.Light propagation off of the turning optic 126 may then contain acomponent perpendicular to propagation along the optical waveguide 12.

After the turning optic 126 directs light to propagate along thevertical waveguide 122, the light enters a vertical beam expandingelement 121 that expands the image along the vertical direction. Thevertical beam expanding element 121 contains components that may be usedto deflect light through a range of angles in the vertical direction.Such components may provide for rays to propagate at a faster rate ascompared to other rays propagating solely in the vertical direction, andas such, the image may be expanded in the vertical direction. Componentsof the vertical beam expanding element 121 may include, but are notlimited to, a wavelength compensated beam expander of similarcomposition to that of the wavelength compensated beam expander 22 inwaveguide 12, one or more mirrors of which at least two must be curved,and/or TIR reflections between the walls of vertical waveguide 122. Thevertical waveguide 122 may be similar in construction to the compensatedbeam expander 22. In some embodiments, a 45 degree deflection may becreated in a vertical direction by turning optic 126 providing light topropagate between walls of the vertical waveguide 122 employing TIR.

In some embodiments, one or more of the components may possess thecapability to change the image forming properties of the componentthrough the application of an electric field. The components may possessstructure similar to optical element 96 in the optical waveguide 12,including a material possessing a refractive index that varies with theapplication of an applied electric field and piezoelectric devicesplaced between the component and the wall of vertical waveguide 122. Thechange in image forming properties allows the vertical beam expandingelement 121 to alter the divergence of the light traveling alongvertical waveguide 122 which may change the perceived distance of anobject from the viewer, either as an independent control or incombination with the second refractive element 86.

In some embodiments, the vertical waveguide 122 may be formed of anoptically clear material having sufficiently high index of refraction toprovide for total internal reflection over a wide range of incidentangles. Potential materials include, but are not limited to, opticalplastic, optical glass, and/or the like. For example, one or moreoptical plastics may be used to reduce cost and/or weight of the opticaldisplay system 10. Thickness of the vertical waveguide 122, angle ofdeflection created by the turning optic 126, and/or spacing of thereflecting elements 124 may determine magnification achieved between theturning optic 126 and the reflecting elements 124.

The reflecting elements 124 may be designed to direct a fraction of theoptical power propagating within the vertical waveguide 122 towards auser's eye at a specific angle and/or specific divergence, independentof the wavelength incident on the reflecting elements 124. Thereflecting element 124 may maintain color balance (ratio) in theoriginal image due to its wavelength independent reflection properties.The reflecting element 124 may include, but is not limited to, aFabry-Perot filter, a partially reflecting thin film element, and/or thelike.

The Fabry-Perot filter may have low reflectivity at end surfaces and asufficiently small distance between such end surfaces, such that therange of wavelengths between resonances of the filter exceeds the rangebetween the blue and red wavelengths contained in the image projected bythe image generator 14. Low reflectivity surfaces may increasetransmission coefficient in a region between resonance wavelengths ofthe filter, thereby reducing the reflectance. Changing surfacereflectivity subsequently may change the reflectance. To ensure thateach reflector in the array delivers substantially similar (i.e., withina few percent and up to 20% difference, for example) optical power tothe user, the reflectance may be configured to begin at a lower valuefor the first reflector and increase steadily for each subsequentreflector in the series chain, since the incident power on eachsubsequent reflector has been reduced by the reflecting operation of theprevious reflector. The reflectance of the first reflector and eachsubsequent reflector depends on the number of reflectors. For example,in the case of four reflectors, the first reflector would reflect 0.25of the incident light, the next reflector would reflect ⅓^(rd) of theremaining light transmitted through the first reflector, the thirdreflector would reflect 0.5 and the final reflector would reflect allincident light, resulting in each reflector directing ¼^(th) of theoriginal power to the user's eye. As the distance between the endsurfaces decreases, the distance between resonant wavelengths increases,and the reflectance as a function of wavelength may closely approximate((i.e., within a few percent and up to 20% difference, for example) aconstant in the region between the resonant wavelengths, resulting inless wavelength dependence in the fraction of power reflected toward theuser. The Fabry-Perot filter may consist of, but is not limited to, amaterial of different index than the surrounding waveguide inserted intothe waveguide, an air gap created by slicing the waveguide and shiftingone side of the slice a specified distance from the other slice, orslicing the waveguide at two nearly adjacent points, applying areflecting thin film to the slice surfaces, and reassembling the slicedparts into a single waveguide.

The reflecting element 124 may also include a partially reflecting thinfilm element. The partially reflecting thin film element may beconfigured to obtain a given reflection coefficient at each wavelength.In some embodiments, the vertical waveguide 122 may be sliced with endsof the slices polished. A thin film may then be applied to each polishedend with the vertical waveguide 122 splice together into a wholecomponent.

The angle at which the reflecting element 124 deflects light toward theuser may be determined by the angle of the reflecting element 124 withrespect to the walls of the vertical waveguide 122 and with respect tothe angle of propagation of the light within the vertical waveguide 122.In some embodiments, the angle of each reflecting element 124 may beconfigured to be different, such that each reflecting element 124directs light into the user's eye from a different direction. Forexample, a first reflecting element 124 may directs light downward at arelatively steep angle, the second reflecting element 124 may directlight downward at a shallow angle, the third reflecting element 124 maydirect light upward at a shallow angle, and the fourth reflectingelement 124 may direct light upward at a relatively steep angle. As afurther example, the reflecting elements 124 on the left side ofvertical waveguide 122 may also possess some horizontal tilt, directinglight back toward the right, and the reflecting elements 124 on theright side of vertical waveguide 122 may possess a different horizontaltilt directing light back toward the left. Varying the direction in sucha way effectively increases the FOV by directing light from a large areaof the vertical waveguide 122 (FOV is highly dependent on the emittingarea) and increasing the range of angles at which light from the imagereaches the eye (increases the FOV further, beyond that resulting fromthe size of the emitting area). Other orientations and positioning ofthe reflecting elements 124 along the vertical direction are possible,depending on the targeted application.

FIG. 14 illustrates a graph 130 of output of an exemplary embodiment ofthe output coupling and vertical expansion system 24. In particular,FIG. 14 illustrates image formation and reflection operation ofreflecting elements 124 for the blue wavelength 76. Generally, imagesform at relatively large distances from the optical waveguide 12. Suchdistances increase as divergence of the beam exiting the output couplingand vertical expansion system 24 approaches zero (i.e., collimatedcondition). It should be noted that positioning of the reflectingelements 124 may be dependent on size restrictions imposed by theapplication, including distance common to a human head and human eye.

FIG. 15 illustrates a graph 132 of a guided beam striking the reflectingelements 124 along the length of the vertical waveguide 122. Thepercentage of power reflected may depend on the incident angledetermined by the angle at which light travels along the verticalwaveguide 122 and the angle of the reflective element 124. Thedivergence of rays exiting from the output coupling and verticalexpansion system 24 may be different from the divergence within thevertical waveguide 122 if surfaces of the reflecting elements 124 arenot flat, but instead configured with a degree of curvature. Curvaturemay alter the reflecting element 124 and as such provide a low power(i.e., long focal length) mirror, for example. As the reflectioncoefficient of a Fabry-Perot filter, for example, depends on angle ofincidence, according to cos(⊖), curvature of the reflecting surface maylimit the range of incident angle to the range wherein cos(⊖)≈1. In someembodiments, collimated light propagating within the vertical waveguide122 may strike one or more reflecting elements 124 configured to createa divergent beam that creates a virtual image for the user at a designeddistance, such as the near point of the user's eye. Changes in thedivergence of the light propagating within the vertical waveguide 122,configuration of adjustments to focal length of the diffraction enhancedimaging system 16 may create greater or less divergence of light fromthe reflecting elements 124 thus changing location of the virtual imageand providing a more natural and/or comfortable viewing experience for auser.

What is claimed is:
 1. An optical display system for providingthree-dimensional convergence corrected images to a user, comprising: atleast two image generators producing a plurality of rays forming aplurality of images; a diffraction enhanced imaging system configured tocollect rays produced by the image generators and configured to controlconvergence angle of each ray at specific wavelengths into an opticalwaveguide such that rays at different wavelengths have differentconvergence angles; an in-coupling diffraction system configured tocouple the rays controlled by the diffraction enhanced imaging systeminto the optical waveguide via at least one of specific convergenceangles and a specific divergence angle; a wavelength compensated beamexpander configured to simultaneously expand horizontal extension of theimages and compensate for wavelength dispersion; and, an output couplingand vertical expansion system configured to magnify the images in avertical direction and direct a fraction of light toward the user at oneor more specific angles creating a wide field of view.
 2. The opticaldisplay system of claim 1, wherein the in-coupling diffraction systemuses diffraction to couple the rays into the optical waveguide atspecific convergence angles such that at least one of the wavelengthcompensated beam expander and the output coupling and vertical expansionsystem produce an expanded beam of the rays having specific divergenceangles.
 3. The optical display system of claim 1, wherein the wavelengthcompensated beam expander simultaneously expand horizontal extension ofthe images and compensate for wavelength dispersion such that colorcomponents of each image pixel of each image overlap precisely at theoutput coupling and vertical expansion system.
 4. The optical displaysystem of claim 1, further comprising: a headset including a framehaving at least one portion configured to rest on at least one of a noseor ear of the user, the frame having a front support element, whereinthe at least two image generators are positioned on the front supportelement to provide a separate image to each eye of the user.
 5. Theoptical display system of claim 4, wherein the diffraction enhancedimaging system includes at least one lens positioned in the frame of theheadset, the lens comprising at least one diffractive portion and atleast one refractive portion configured to alter wavelength dispersioneffect on image distance produced by the lens.
 6. The optical displaysystem of claim 5, wherein the lens comprises: a first substrate layerformed of an optically clear material having known wavelength dispersionproperties; a first diffractive grating layer positioned adjacent to thefirst substrate layer, the first diffractive grating layer is formed ofa holographic material and includes a plurality of gratings, thegratings configured with a grating period impacting wavelengthdispersion; a second diffractive grating layer positioned adjacent tothe first diffractive grating layer and formed of substantially similarmaterial and properties as the first diffractive grating layer, thesecond diffractive grating layer having a plurality of gratings; and, asecond substrate layer positioned adjacent to the second diffractivegrating layer and formed of an optically clear material.
 7. The opticaldisplay system of claim 6, the lens further comprises a spacer layerformed of an optically clear material and positioned between the firstdiffractive grating layer and the second diffractive grating layer. 8.The optical display system of claim 6, wherein the first substrate layerincludes a first surface and a second surface and at least one of thefirst surface and the second surface is a curved surface.
 9. The opticaldisplay system of claim 6, wherein the second substrate layer includes afirst surface and a second surface and at least one of the first surfaceand the second surface is a curved surface.
 10. The optical displaysystem of claim 6, wherein peaks of the gratings of the seconddiffractive grating layer lie at a substantially similar position asvalleys of the gratings of the first diffractive grating layer.
 11. Theoptical display system of claim 6, wherein at least one of the firstsubstrate layer, first diffractive grating layer, second diffractiongrating layer and second substrate layer consist of at least onematerial having a refractive index configured to be controlled byapplication of an electric field.
 12. The optical display system ofclaim 6, further comprising a wedge element configured to provide atleast one image at a different angle from an optical axis of the lensand a different distance from an output plane of the lens.
 13. Theoptical display system of claim 6, further comprising a refractiveelement positioned adjacent to the lens, the refractive element beingformed of dispersive material and configured to enhance wavelengthdispersion of the lens.
 14. The optical display system of claim 1,wherein the in-coupling diffraction system includes a single diffractiongrating having a period configured to direct rays entering thein-coupling diffraction system to exit the in-coupling diffractionsystem at an angle conducive to propagation within the optical waveguideby total internal reflection.
 15. The optical display system of claim14, wherein period of the single diffraction grating alters ray cone foreach wavelength to create a new image point configured as an input imagefor the wavelength compensated beam expander.
 16. The optical displaysystem of claim 14, wherein period of the single diffraction grating isconfigured to modify wavelength dispersion introduced by the diffractionenhanced imaging system.
 17. The optical display system of claim 1,wherein distance between the diffraction imaging system and thein-coupling diffraction system is determined such that beam width foreach color at an input plane of the in-coupling diffraction system andaxis of beams intercepting the in-coupling diffraction system results ina beam of light that includes wavelengths having substantially similarbeam width and beam axis when exiting the wavelength compensated beamexpander.
 18. The optical display system of claim 1, wherein thein-coupling diffraction system includes multiple diffraction gratingswith each grating tuned to one of three RGB colors such that eachdiffraction grating controls imaging properties of each wavelength. 19.The optical display system of claim 1, wherein the wavelengthcompensated beam expander includes at least two optical elementspositioned in series and each configured to alter wavelength dispersionproperties of rays.
 20. The optical display system of claim 19, whereina first image produced by a first optical element is an input image fora second optical element.
 21. The optical display system of claim 20,wherein the second optical element may be configured to producecollimated light for each wavelength with position and propagationdirection of each output beam overlapping with beams for otherwavelengths.
 22. The optical display system of claim 19, wherein eachoptical element includes at least one of a reflective mirror, asingle-axis Fresnel reflector, and a reflection grating.
 23. The opticaldisplay system of claim 1, wherein the output coupling and verticalexpansion system includes a vertically oriented waveguide having atleast two reflecting elements configured to magnify images in a verticaldirection and direct at least a fraction of light out of the verticallyoriented waveguide and towards the user at specific angles to create thewide field of view.
 24. A method, comprising: collecting a plurality ofrays forming images produced by a plurality of image generators andaltering convergence angle of the rays at each wavelength such that raysat different wavelengths have different convergence angles; coupling therays into an optical waveguide system using diffraction at specificconvergence and divergence angles; expanding horizontal extent of eachimage; compensating for wavelength dispersion such that color componentsof each image pixel overlap; magnifying each image in a verticaldirection; and, directing a fraction of light out of the opticalwaveguide system and toward a user at specific angles to create a widefield of view.
 25. An optical display system, comprising: at least twoimage generators producing a plurality of rays forming a plurality ofimages; and, a diffraction enhanced imaging system configured to collectrays produced by the image generators and configured to controlconvergence angle of each ray at specific wavelengths into an opticalwaveguide such that rays having different wavelengths have differentconvergence angles, the diffraction enhanced imaging system comprising alens having at least one diffractive portion and at least one refractiveportion configured to alter wavelength dispersion effect on imagedistance produced by the lens.